This invention relates to a method for preparing a coated powder, more particularly to a method for preparing a coated powder in which an aluminum nitride powder is coated with silicon carbide.
In recent years, much attention has been paid to using a sintered aluminum nitride (AIN) body as a high-temperature material because of its excellent heat resistance, thermal shock resistance and thermal conductivity. The sintered aluminum nitride body, however, has somewhat chemically unstable properties, especially since it reacts with water to produce ammonia when converted into an oxide. For this reason, the sintered body cannot comprise to any structural member which is required to be chemically stable for a long period of time. Particularly, the aluminum nitride powder which is a raw material for the sintered body brings about the above-mentioned phenomenon and is also considered to cause some trouble when added to a resin as a filler.
With the aim of solving such problems above, the present applicants have already suggested, in a patent application, a composite ceramic powder in which a silicon carbide powder is coated with aluminum nitride and which has a chemical stability and a good thermal conductivity (see Japanese Provisional Patent Publication No. 91059/1983). As one manufacturing example of such a coated powder, a coating method is disclosed which comprises externally adding active aluminum and nitrogen to the silicon carbide powder and depositing aluminum nitride on surfaces of the silicon carbide powder particles. A vapor phase method may be used as a method for adhering aluminum nitride on surfaces of the silicon carbide. However, this method presents the technical difficulty that the aluminum nitride can not be completely coated to each of the silicon carbide powder particles, and if the coating is not complete, electrical characteristics of the sintered body could not be satisfied.
An object of this invention is to provide a method capable of preparing in a manner of mass production a chemically stable composite ceramic powder where an aluminum nitride powder is coated, on each surface thereof, with a uniform silicon carbide film having enough thickness.